This invention relates to a process for producing a zeolite adsorbent with a metal ferrocyanide for separating and concentrating cesium from a radioactive liquid waste, etc., and also to a process for treating a radioactive liquid waste, particularly a liquid waste containing radioactive cesium generated from radioactive material-handling facilities.
Treatment of radioactive liquid waste is always a problem in the field of developing and utilizing atomic energy.
Radioactive cesium is produced in a large amount by nuclear fission reaction of uranium-235, etc. For example, the radioactive cesium produced by nuclear fission includes, for example, cesium-137 (nuclear fission yield: 6.2%; half life: 30 years), cesium-135 (nuclear fission yield: 6.4%; half life: 3.times.16.sup.6 years), cesium-133 (nuclear fission yield 6.6%; stable) and cesium-134 (half life: 2.3 years) produced by radioactivation of cesium-133 by neutrons. The radioactive cesium has a long half life and is an alkali metal, and thus is dissolved in cooling water for nuclear reactor. Accordingly, a liquid waste from regeneration of a condensate demineralizer of nuclear reactor contains the radioactive cesium. Also, a liquid waste from a nuclear fuel reprocessing plant contains the radioactive cesium. That is, various liquid wastes from nuclear reactors and related facilities contain the radioactive cesium, and thus it is very important to remove the radioactive cesium in the treatment of the liquid wastes.
Well known processes for removing the radioactive cesium from radioactive liquid waste generated from the radioactive material-handling facilities such as nuclear power plant, etc. include an evaporation-separation process for treating liquid wastes in an evaporator, a process for ion exchange adsorption with ion exchange resin or inorganic ion exchanger, for example, zeolite [M. Horioka: Nippon Genshiryoku Gakkai-shi 11 10 (1969)], a process for coprecipitation with nickel ferrocyanide [N. Furuya: Technical Report of Kyoto University Nuclear Reactor Laboratory KURRI-Th-73 (1970)], and a process for cesium removal with copper ferrocyanide-impregnated anion exchange resin, i.e. ion exchange resin with improved adsorption characteristics [Journal of Nuclear Science and Technology 4 (4) 190-194 (April, 1967)]. Also, it has been reported that sparingly water-soluble ferrocyanides have such a characteristic as to take cesium ions into the crystal lattice of the ferrocyanide [Barton, etc: Ind. Eng. Chem. 50 212 (1958)].
However, the evaporation-separation process cannot attain a high percent cesium removal due to mist entrainment, and the coprecipitation process is so complicated in operation that a high percent cesium removal is very hard to obtain by one treatment.
The cesium removal with ion exchange resin or inorganic ion exchanger has a high percent cesium removal from a simple laboratory test solution, that is, an aqueous solution containing no other metal ions or cations than cesium ions, but the actual radioactive liquid waste generated from the nuclear material-handling facilities contains other coexisting metal ions and cations than cesium ions, particularly a relatively large amount of sodium ions, as shown in Table 1, and the cesium adsorption is so inhibited by these coexisting metal ions that it is hard to obtain a high percent cesium removal. Ion exchange resin is also poor in heat resistance, acid resistance and alkali resistance. Any of these well known processes has problems.
TABLE 1 ______________________________________ Concentra- Nuclear material- Main tion (% by handling facilities component weight) ______________________________________ Nuclear Boiling water Na.sub.2 SO.sub.4 15-25 power plant type nuclear based on reactor (BWR) light Pressurized Na.sub.2 B.sub.4 O.sub.7 2-5 water water type nuclear nuclear reactor reactor (PWR) Nuclear fuel-reprocessing plant NaNO.sub.3 20-50 ______________________________________